1. Technical Field
The present invention relates to a conductive paste, a printed circuit board using the conductive paste, and to a method of manufacturing the printed circuit board.
2. Description of the Related Art
Conductive adhesive, used in mounting components onto a substrate or in interconnecting electrodes, has the purpose of securing and electrically connecting an object. As such, a typical form of conductive adhesive has conductive metal particles, such as of silver or copper, etc., dispersed in a paste of viscous resin or hardening resin.
For proper adhesion, it is important that the adhesive and the surface of the object being attached be sufficiently close together, to the level of micrometers. In the case of a viscous type resin, the resin commonly used is one that is readily altered into a moldable state, whereas in the case of a hardening type resin, the resin commonly used is one that has high fluidity and high wetting properties.
As such, in either case of using a viscous type or hardening type resin, the adhesive can flow into the micro-level irregularities in the object being attached, and can thus provide adequate adhesion.
The conductive particles may have various shapes according to their usage. In either case of the viscous type or hardening type resin, since a low resistance is required for adequate electrical connection, it may be needed to increase the content of conductive particles within the adhesive, remove bubbles, and increase the volume occupied by the conductive materials.
In the conductive adhesive of the related art, the conductivity is maintained by contact between the conductive particles. Here, stress may be created, such as when the object being attached is expanded or contracted by heat, or when the board to which the adhesive is applied is bent. When the stress is relieved, the contact between particles can become misadjusted, whereby the resistance can be increased.
The conductive paste currently used for interlayer connection generally has the form of a mixture of polymers and silver particles. The conductive paste can be used to form bumps on an aluminum board, by repeating the printing process until the bumps are formed to a target height and shape. With this kind of paste, conical bumps of a desired height and diameter may typically be formed after repeating the printing four to five times.
Afterwards, drying and penetration processes can be used to implement the connection between layers. In the above series of processes, the repeated printing of the paste can lead to delayed process times, complicated processes, and a greater risk of the bumps spreading.